This invention relates to a method of controlling intake air quantity for internal combustion engines at idle, and more particularly to a method of this kind which is capable of accurately controlling the intake air quantity when the engine is idling at a low atmospheric pressure, such as at a high altitude.
A conventional idling speed feedback control method for internal combustion engines has been known, which is adapted to electronically control a control valve for regulating the quantity of supplementary air to be supplied to the engine during idling through an air passage communicating at one end with an intake passage of the engine at a location downstream of a throttle valve therein and another end with the atmosphere, in a manner responsive to the difference between actual engine speed and desired idling speed set based, e.g. upon load on the engine.
Further, a conventional method of controlling intake air quantity for internal combustion engines has been known, wherein the engine is provided with a fast idling control device which is operated by mechanical actuator means to supply the engine with supplementary air in quantities responsive to the engine temperature through an air passage bypassing the throttle valve when the engine is in a cold state, so that the intake air quantity can be controlled to values suitable for improving the stability of idling of the engine in a cold state.
Furthermore, an intake air quantity control method for an internal combustion engine has been proposed, e.g. by Japanese Provisional Patent Publication (Kokai) No. 59-168238 assigned to the assignee of the present application published on Sept. 21, 1984, wherein the supplementary air quantity to be supplied to the engine is corrected by means of the aforementioned control valve by a correction value dependent upon atmospheric pressure encompassing the engine, so as to control the supplementary air quantity to an appropriate value corresponding to atmospheric pressure. According to this proposed method, the supplementary air quantity is corrected through the control valve in response to atmospheric pressure, by the use of a correction value dependent upon atmospheric pressure, thereby obtaining a supplementary air quantity corresponding to the difference between actual engine speed and desired idling speed and commensurate with atmospheric pressure. However, according to the proposed method, only the supplementary air quantity through the control valve can be corrected in response to atmospheric pressure, but the supplementary air quantity supplied through the fast idling control device is not corrected in response to atmospheric pressure. However, since the valve opening area of the fast idling control device is relatively large as compared with that of the throttle valve during idling, it is an essential requisite to compensate for a shortage and an excess of the supplementary air quantity through the fast idling control device due to a change in the atmospheric pressure so as to control the supplementary air quantity through the device to a value commensurate with atmospheric pressure.